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Background: Flowmotion analysis of the microcirculatory blood flow is a method to extract information about the vessel regulatory function. It has previously shown promise when applied to measurements during a post-occlusive reactive hyperemia. However, the reperfusion peak and the following monotonic decline introduces false low frequencies that should not be interpreted as rhythmic vasomotion effect., Aim: To develop and validate a robust method for flowmotion analysis of post-occlusive reactive hyperemia signals., Method: The occlusion-induced reperfusion response contains a typical rapid increase followed by a monotonic decline to baseline. A mathematical model is proposed to detrend this transient part of the signal to enable further flowmotion analysis. The model is validated in 96 measurements on healthy volunteers., Results: Applying the proposed model corrects the flowmotion signal without adding any substantial new false flowmotion components., Conclusion: Future studies should use the proposed method or equivalent when analyzing flowmotion during post-occlusive reactive hyperemia to ensure valid results., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Objectives: Laser Doppler Flowmetry (LDF) is a non-invasive technique for the assessment of tissue blood flow, but increased reproducibility would facilitate longitudinal studies. The aim of the study was to assess the interday reproducibility of Laser Doppler Flowmetry (LDF) at rest, at elevated local temperatures, and with the use of the vasodilator Methyl Nicotinate (MN) in six interconnected protocols for the measurement of the blood supply to the microvascular bed of the gingiva., Methods: Ten healthy volunteers were included. Interweek LDF measurements with custom-made acrylic splints were performed. Six protocols were applied in separate regions of interest (ROI): 1; basal LDF, 2; LDF with thermoprobe 42 °C, 3; LDF with thermoprobe 45 °C, 4; LDF with thermoprobe 42 °C and MN, 5; LDF with thermoprobe 45 °C and MN and 6; LDF with MN., Results: Intra-individual reproducibility was assessed by the within-subject coefficient of variation (wCV) and the intraclass correlation coefficient (ICC). Basal LDF measurements demonstrated high reproducibility with wCV 11.1 in 2 min and 10.3 in 5 min. ICC was 0.9 and 0.92. wCV after heat and MN was 4.9-10.3 and ICC 0.82-0.93. The topically applied MN yielded increased blood flow., Conclusion: This is the first study evaluating the reproducibility of basal LDF compared to single or multiple vasodilatory stimuli in gingiva. Multiple collector fibers probe and stabilizing acrylic splints are recommended. Vasodilatory stimulation showed a tendency toward higher reproducibility. Furthermore, MN yields vasodilation in gingiva., Competing Interests: Declaration of competing interest There are no conflicts of interest reported by any of the authors., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: Workload and sex-related differences have been proposed as factors of importance when evaluating the microcirculation. Simultaneous assessments with diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) enable a comprehensive evaluation of the microcirculation. The aim of the study was to compare the response between sexes in the microcirculatory parameters red blood cell (RBC) tissue fraction, RBC oxygen saturation, average vessel diameter, and speed-resolved perfusion during baseline, cycling, and recovery, respectively., Methods: In 24 healthy participants (aged 20 to 30 years, 12 females), cutaneous microcirculation was assessed by LDF and DRS at baseline, during a workload generated by cycling at 75 to 80 % of maximal age-predicted heart rate, and recovery, respectively., Results: Females had significantly lower RBC tissue fraction and total perfusion in forearm skin microcirculation at all phases (baseline, workload, and recovery). All microvascular parameters increased significantly during cycling, most evident in RBC oxygen saturation (34 % increase on average) and perfusion (9-fold increase in total perfusion). For perfusion, the highest speeds (>10 mm/s) increased by a factor of 31, whereas the lowest speeds (<1 mm/s) increased by a factor of 2., Conclusion: Compared to a resting state, all studied microcirculation measures increased during cycling. For perfusion, this was mainly due to increased speed, and only to a minor extent due to increased RBC tissue fraction. Skin microcirculatory differences between sexes were seen in RBC concentration and total perfusion., Competing Interests: Declaration of competing interest Dr. Fredriksson is part-time employed by Perimed AB, which is developing products related to research described in this publication., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Competing Interests: Declaration of competing interest Dr. Hultman and Dr. Fredriksson are part-time employed by Perimed AB, which is developing products related to research described in this publication.

Chronic limb-threatening ischemia (CLTI) has a major impact on patients' lives and is associated with a heavy health care burden with high morbidity and mortality. Treatment by endovascular intervention is mostly based on macrocirculatory information from angiography and does not consider the microcirculation. Despite successful endovascular intervention according to angiographic criteria, a proportion of patients fail to heal ischemic lesions. This might be due to impaired microvascular perfusion and variations in the supply to different angiosomes. Non-invasive optical techniques for microcirculatory perfusion and oxygen saturation imaging have the potential to provide the interventionist with additional information in real-time, supporting clinical decisions during the intervention. This study presents a novel multimodal imaging system, based on multi-exposure laser speckle contrast imaging and multi-spectral imaging, for continuous use during endovascular intervention. The results during intervention display spatiotemporal changes in the microcirculation compatible with expected physiological reactions during balloon dilation, with initially induced ischemia followed by a restored perfusion, and local administration of a vasodilator inducing hyperemia. We also present perioperative and postoperative follow-up measurements with a pulsatile microcirculation perfusion. Finally, cases of spatial heterogeneity in the oxygen saturation and perfusion are discussed. In conclusion, this technical feasibility study shows the potential of the methodology to characterize changes in microcirculation before, during, and after endovascular intervention., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

The objective of this study was to explore the associations between skin microcirculatory function and established cardiovascular risk factors in a large Swedish cohort. As part of the Swedish CArdioPulmonary bioImage Study (SCAPIS), microcirculatory data were acquired at Linköping University hospital, Linköping, Sweden during 2016-2017. The subjects, aged 50-64 years, were randomly selected from the national population register. Microcirculatory reactivity was assessed using a 5-min arterial occlusion-release protocol. Comprehensive skin microcirculatory data were continuously acquired by using a fiberoptic probe placed on the lower right arm. After exclusion of missing data (208), 1557 subjects were remaining. Among the parameters, skin microcirculatory peak oxygen saturation after occlusion release, had the strongest relationship to the cardiovascular risk factors. The linear associations between peak oxygen saturation and cardiovascular risk factors were analyzed adjusted for age and sex. We found a negative association with peak oxygen saturation (standardized regression coefficient) for blood pressure (systolic -0.05 (95% CI: -0.10;-0.003) and diastolic -0.05 (-0.10; -0.003)), BMI -0.18 (-0.23; -0.13), waist circumference (males -0.20 (-0.32; -0.16), females -0.18 (-0.25; -0.11)), prevalent diabetes -0.31 (-0.49; -0.12), hypertension -0.30 (-0.42; -0.18), dyslipidemia -0.24 (-0.40; -0.09), fasting glucose level -0.06 (-0.12; -0.01), HbA1c -0.07 (-0.12; -0.02), triglyceride level -0.09 (-0.14; -0.04), hsCRP -0.12 (-0.17; -0.07), and current smoker versus never smoked -0.50 (-0.67; -0.34). A positive association with peak oxygen saturation was found for cholesterol level 0.05 (0.005; 0.11) and HDL 0.11 (0.06; 0.17). This is the first study showing that post-ischemic skin microvascular peak oxygen saturation is associated with virtually all established cardiovascular risk factors in a population-based middle-aged cohort., (Copyright © 2021. Published by Elsevier Inc.)

We have developed a new fiber-optic system that combines diffuse reflectance spectroscopy (DRS) and laser Doppler Flowmetry (LDF) for a multi-modal assessment of the microcirculation. Quantitative data is achieved with an inverse Monte Carlo algorithm based on an individually adaptive skin model. The output parameters are calculated from the model and given in absolute units: hemoglobin oxygen saturation (%), red blood cell (RBC) tissue fraction (%), and the speed resolved RBC perfusion separated into three speed regions; 0-1mm/s, 1-10mm/s and above 10mm/s (% mm/s). The aim was to explore microcirculatory parameters using the new optical method, integrating DRS and LDF in a joint skin model, during local heating of the dorsal foot and venous and arterial occlusion of the forearm in 23 healthy subjects (age 20-28years). There were differences in the three speed regions in regard to blood flow changes due to local heating, where perfusion for high speeds increased the most. There was also a high correlation between changes in oxygenation and changes in perfusion for higher speeds. Oxygen saturation at baseline was 44% on foot, increasing to 83% at plateau after heating. The larger increase in perfusion for higher speeds than for lower speeds together with the oxygenation increase during thermal provocation, shows a local thermoregulatory blood flow in presumably arteriolar dermal vessels. In conclusion, there are improved possibilities to assess microcirculation using integrated DRS and LDF in a joint skin model by enabling both oxygenation and speed resolved blood flow assessment simultaneously and in the same skin site. Output parameters in absolute units may also yield new insights about the microcirculatory system., (Copyright © 2015. Published by Elsevier Inc.)

A new method for estimating the measurement depth and volume in laser Doppler flowmetry (LDF) is presented. The method is based on Monte Carlo simulations of light propagation in tissue. The contribution from each individual Doppler shift is calculated and thereby multiple Doppler shifts are handled correctly. Different LDF setups for both probe based (0.0, 0.25, 0.5, and 1.2 mm source-detector separation) and imaging systems (0.5 and 2.0 mm beam diameter) are considered, at the wavelengths 543 nm, 633 nm, and 780 nm. Non-linear speckle pattern effects are accounted for in the imaging system setups. The effects of tissue optical properties, blood concentration, and blood oxygen saturation are evaluated using both homogeneous tissue models and a layered skin model. The results show that the effect on the measurement depth of changing tissue properties is comparable to the effect of changing the system setup, e.g. source-detector separation and wavelength. Skin pigmentation was found to have a negligible effect on the measurement depth. Examples of measurement depths are (values are given for a probe based system with 0.25 mm source-detector separation and an imaging system with a 0.5 mm beam diameter, respectively, both operating at 780 nm): muscle - 0.55/0.79 mm; liver - 0.40/0.53 mm; gray matter - 0.48/0.68 mm; white matter - 0.20/0.20 mm; index finger pulp - 0.41/0.53 mm; forearm skin - 0.53/0.56 mm; heat provoked forearm skin - 0.66/0.67 mm.